Maturity of silicon nanoelectronics and the high quality of 300 mm epi-Si wafers make these substrates an ideal choice for the growth of high quality III-Nitride devices. The results of our substrate engineering technique, which involves implantation of nitrogen into Si through an AlN thin film, have shown to simultaneously and significantly reduce the dislocation density and macro-cracks in epitaxially grown 2 pm GaN films. In this study, high quality strain engineered GaN films were grown by metalorganic chemical vapor deposition (MOCVD) and spectroscopic ellipsometry was used to characterize the dielectric properties, thickness, and stress of the complex structure. The uniaxial, anisotropic dielectric functions of wurtzite GaN and AlN were determined for the processes used in this study, and using this information, the thickness of each layer was determined in the completed film stack. IR spectroscopic ellipsometry (IRSE) was used as the non-destructive characterization technique to identify the IR sensitive phonon modes in AlN. The stress evolution in the films was investigated as a function of the phonon frequency shift and the broadening of the phonon modes. The results obtained by IRSE were further complemented by high resolution X-ray diffraction (HRXRD) and Raman scattering measurements. (C) 2010 Elsevier B.V. All rights reserved.